1. Field of the Invention
The present invention generally relates to a printer. More particularly, the present invention relates to a thermal printer including a frame, a thermal head, a detachable platen roller, and a platen roller drive motor.
2. Description of the Related Art
FIGS. 1, 2, and 3 show a conventional thermal printer 1. In FIGS. 1, 2, and 3, X1-X2 shows the width direction, Y1-Y2 shows the depth direction, and Z1-Z2 shows the height direction of the thermal printer 1. The thermal printer 1 includes a die-cast zinc frame 2. The frame 2 includes a body 3 long in the X direction, sideboards 4 and 5 at the corresponding sides of the body 3, and shafts 6 protruding from the sideboard 4. The sideboards 4 and 5, respectively, have substantially U-shaped bearings 7 and 8 and recesses 9 for holding platen roller holding springs 12 and 13. A paper guide 10, thermal-head-pressing plate springs 11, the platen roller holding springs 12 and 13 made by bending wire springs, and a gearbox cover 14 are fixed to the frame 2. The thermal printer 1 also includes a thermal head 20, a platen roller drive motor 30, a reduction gear train 40, and a platen roller 50.
The thermal head 20 is disposed parallel to the body 3 of the frame 2 with the corresponding ends of the thermal head 20 fitted into the sideboards 4 and 5. The thermal head 20 is biased toward the Y2 direction by the thermal-head-pressing plate springs 11. The platen roller drive motor 30 is fixed to the inner surface of the sideboard 4 and is disposed at the Y1 side of the body 3. Gears constituting the reduction gear train 40 are supported by the shafts 6. The gearbox cover 14 is attached to the X1 side of the sideboard 4 to cover the reduction gear train 40. The platen roller 50 has shafts 51 and 52 protruding from the corresponding ends. Bearing parts 53 and 54 fitted around the shafts 51 and 52 are placed in the bearings 7 and 8, respectively. The platen roller holding springs 12 and 13, respectively, press the bearing parts 53 and 54 and thereby hold them in the bearings 7 and 8. Thus, the platen roller 50 is detachably attached to the frame 2.    [Patent document 1] Japanese Patent Application Publication No. 2005-059395
Conventionally, frames of thermal printers are produced by die-casting. This makes it necessary to remove burrs formed during the die-casting process from the frames. Furthermore, burrs that cannot be removed by abrasive blasting have to be removed manually. Thus, producing a frame of a thermal printer by die-casting increases the number of steps and the workload to produce the thermal printer.
Also, producing a frame by die-casting may cause porosity in the frame which results in reduced strength of the frame.
In addition, die-casting dies are expensive and therefore increase the equipment cost.
Further, using a die-cast frame increases the number of parts of a thermal printer. For example, the conventional thermal printer 1 described above requires the paper guide 10, the thermal-head-pressing plate springs 11, and the platen roller holding springs 12 and 13 in addition to the frame 2.